Originally published in The Manitoban, 2011
Ah,
time to go back to school. If you're anything like me you've probably
bought a bunch of new pens and stationary you don't really need and
have resolved to read your textbooks and class notes every day, maybe
even get up extra early before classes to do something physically
healthy. Soon enough though, as the first 2011 semester kicks into
high gear, most of us are bound to feel as exhausted as though the
life were being sucked right out of us. That's why I have chosen to
begin the first fall issue of The Manitoban
by telling you about the parasitic wasp Dinocampus
coccinellae.
D. coccinellae
is found throughout Eurasia and North America and parasitizes
numerous species of lady beetles (your friendly, aphid-eating, garden
variety “lady bug”). Females mate with males as infrequently as possible. A queen will store the sperm from a single mating for up to one year, using this sperm to fertilize eggs and produce sterile female workers which she uses to build her colony. When the sperm begins to run out, fertile males and females are produced and these disperse to form new colonies.
Thus, males are rarer than females, although they are
produced every once in awhile so they can disperse, mate, and contribute to the genetic diversity of the species via sexual
reproduction.
The
wasps preferentially parasitize female lady beetles and do so by
injecting an egg directly into the beetle's body cavity. Once the egg
hatches, the larva eats the lady beetle's own eggs in order to
nourish itself and eliminate competition for nutrients. Once the eggs
have all been eaten, the larva begins to eat it's lady beetle host's surrounding body
tissue, including her reproductive structures.
After
about 20 days the larva is ready to emerge. This is achieved by
chewing a hole through the lady beetle's body. Then, the larva is
ready to spin a coccoon inside which it will metamorphose into an
adult wasp. The larva spins its coccoon within the hind limbs of the
lady beetle, who is paralyzed, still alive and probably very
miserable.
Currently
unidentified venoms secreted by the wasp larva are believed to be
responsible for the next stage in this ghastly business.
The lady beetle, paralyzed with a wasp coccoon under her body, is now
also a victim of behavioural modification courtesy of the wasp—the
beetle begins to twitch and grasp erratically. This behaviour, along
with the familiar red and black colouration of the lady beetle,
serves to ward off predators,
thus protecting the developing larva.
Many
species of parasitic wasps lay eggs in a variety of host species;
however, most of these lead to the death of the host. Not so with D.
coccinellae, although I bet the
lady beetles wish they were dead. After the adult wasp emerges from
its coccoon, the effects of paralysis wear off, as does the
behavioural control exerted by the larva. Approximately 25% of
parasitized lady beetles survive this process and presumably amble
off to continue their regular lady beetle duties, albeit with gored reproductive organs and a pretty wicked hole in the undercarriage.
Yet
leaving the host alive is not without costs of its own. After all,
nothing in life is truly free, right? Researchers at Laboratoire
Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution
et Contrôle (CNRS/IRD/Université Montpellier) and the Université
de Montréal were able to show that while wasp larvae guarded by lady
beetles are less likely to experience predation, they also lay fewer
eggs
(Maure et al. 2011). The developing larvae lose resources by keeping
the lady beetle alive, resulting in the observed reduction in
fecundity of the adult wasps. Maure et al. (2011) showed that while
larvae without lady beetle protection are more likely to experience
predation, those that survive lay more eggs on average than wasps
with a lady beetle bodyguard.
So when the term
hits full swing remember—you don't have it half as bad as the
spotted lady beetle does!
No comments:
Post a Comment